Experimental and clinical data suggest that alloreactive NK cells can reduce the risk of graft-rejection, GvHD and leukemic relapse after HLA-mismatched transplantation. The effectiveness of allogeneic NK cells is a function of HLA-differences between donor and recipient that give rise to NK cell clones which do not express inhibitory receptors matching for the HLA molecules of the recipient. Aim of the study is to evaluate cellular therapy with alloreactive, IL-2 activated NK cells after transplantation of T-cell depleted stem cell grafts from one haplotype mismatched family donors in patients with hematological malignancies.